1. Field of the Invention
The invention relates to a system for detecting one or more vehicles, such as a train, on a rail track, including at least one optical conductor extending near and parallel to the rail track with a light source and light detector coupled thereto, and one or more sensors coupled to the rail track and including the light conductor, which sensors affect the light attenuation in the light conductor locally upon the presence of the vehicle.
2. The Prior Art
A detection of the presence of a train on a particular railway section has in the past been effected by employing electromagnetic detection means. Thus, for example, the short circuit between rail, which is caused by the wheels and the axles of train sets, was detected and employed, for example, for the automatic operation of a railway crossing. A drawback of such electrical-engineering means, however, is that such short circuits may also arise from other causes, for example, if it rains or if salt is applied. Moreover, the electromagnetic relays employed can be adversely affected by the electric and magnetic fields which are generated within the trains themselves.
Optical train detection means have the advantage that their operation is not affected, or is barely affected, by weather conditions or electromagnetic interference fields. For this reason, optical detection systems have been proposed previously, in which an optical conductor is disposed along a rail, and suitable sensors affect the transmission of light depending on the presence of a train. Thus, for example, optical bending detectors are known which detect the sag of a rail between two sleepers when a train is passing. The sensitivity of such bending detectors is generally not satisfactory, however.
Another proposal was to arrange pressure detectors between the rail and the sleeper or in the rail bed, such as is indicated in DE 3815152 A1. In a pressure detector of this type, the optical conductor, under the influence of a train wheel, is compressed to a certain extent, which results, for example, in part of the transmitted light being coupled from the optical conductor into another optical conductor. The light coupled into the other optical conductor is used to detect the presence of pressure and thus of a train. A pressure detector of this type has the drawback, however, that the optical conductor itself is repeatedly deformed quite strongly, which may lead, in particular, to damage of the coating of the optical conductor. The service life of the optical conductor, such as a glass fibre, is therefore relatively short in known pressure detectors of this type. Moreover, a supplementary optical conductor is required to transmit the extracted light to detection equipment.